http://mepopedia.com/forum/list.php?571 Wed, 29 Apr 2026 15:47:29 +0800 Phorum 5.2.7 http://mepopedia.com/forum/read.php?571,19932,19932#msg-19932 http://mepopedia.com/forum/read.php?571,19932,19932#msg-19932 資料來源：法國國家科學研究中心 (CNRS)

天文學家發現五十顆系外行星 (Cinquante nouvelles exoplanètes découvertes)

由法國國家科學研究中心（CNRS）、巴黎第六大學（UPMC）及凡爾賽大學（UVSQ）組成的國際天文學家團隊，於2011年9月12日宣佈發現50顆圍繞鄰近恆星運轉的系外行星。這個豐富的發現得歸功於歐洲南方天文台（ESO）強大的系外行星搜尋儀器HARPS。這次發現的系外行星包括16顆超級地球，其質量為地球的1至10倍。其中一顆超級地球位於其恆星系的適居帶，可能有利於生命的出現及演進。研究員也確定，40％以上的類太陽恆星系中，至少有一顆行星比土星輕。這些新發現於9月12日在美國懷俄明州舉行的太陽系外（Extreme Solar Systems）研討會上發表。

HARPS獵星器自2003年起開始在南半球的天空中尋找環繞太陽以外之恆星運轉的行星。HARPS獵星器有一部份是在法國開發的，裝設於智利歐洲南方天文台的La Silla觀測台上，是全球性能最佳的系外行星搜尋器。到目前為止，它已經透過高精度的恆星徑向速度測量技術*1，發現了100多顆系外行星*2，如今又發現50顆新行星。HARPS此次的新發現豐富，包括16顆超級地球*3 及類似海王星*4 的行星繞著類太陽的恆星運轉。

天文學家利用HARPS獵星器進行觀察，能更加精確估計環繞類太陽恆星運轉的低質量行星（不像大量氣體組成的木星或土星）。他們發現，這些類太陽恆星系有40％以上都有至少一顆質量小於土星（質量是地球的3至100倍）的行星。

HARPS獵星器可望達到前所未有的穩定性及靈敏度，能在未來幾年搜尋可能蘊藏生命的岩質行星。天文學家選出10顆鄰近的類太陽恆星*5，以便進行超級地球的系統性研究。他們費時兩年發現5顆質量比地球小5倍的行星，其中一顆可能有生命存在。HARPS獵星器迄今已發現2顆位於適居帶（在恆星周圍、有液態水存在的狹窄地帶）的超級地球。第一顆是2007年發現的Gliese 581 d；第二顆是HD 85512 b，位於36光年之遙，其質量約為地球的3.6倍，是HARPS獵星器發現的行星中質量最小的。HARPS獵星計畫主持人Michel Mayor表示，「HD 85512 b的發現，顯示我們有可能在類太陽恆星系的適居帶內發現其他超級地球。」他與日內瓦天文台的Stéphane Udry共同執行該計畫。

天文學家預計20年內應該可以公布第一份鄰近太陽系的適居行星列表。有了這份列表，未來將能在系外行星的大氣中尋找可能的生命光譜信號。這些結果讓天文學家更加確信在不久的將來，就能發現其它圍繞類太陽恆星的岩質小行星。這部分的研究需要新儀器的協助，包括上普羅旺斯天文台的SOPHIE光譜儀、裝設在加納利群島之義大利伽利略望遠鏡上的仿HARPS獵星器（用以研究北半球天空的星體），以及預計於2016年裝設在智利歐洲南方天文台超大型望遠鏡VLT上、性能更強的星體搜尋器ESPRESSO。

本次觀察結果已於9月12日在美國懷俄明州舉行的太陽系外研討會上發表。逾350名系外行星專家出席該會。

HARPS團隊成員包括來自瑞士日內瓦天文台（OAUG）的Michel Mayor、M. Marmier、C. Lovis、S. Udry、D. Ségransan、F. Pepe、X. Dumusque、D. Queloz，以及瑞士伯恩大學物理研究所的W. Benz、法國大氣環境暨太空觀測實驗室的Jean-Loup Bertaux、巴黎天文物理學研究所的François Bouchy，（CNRS/UPMC）、法國上普羅旺斯天文台、歐洲南方天文台德藉研究員G. LoCurto、德國馬克斯．普朗克研究院的C. Mordasini、葡萄牙Porto大學天文物理學中心的N.C. Santos。

註釋(*)：
*1) 利用該技術，天文學家可以估計行星的最小質量。HARPS獵星器以每小時3.5公里的高精度測量恆星的徑向速度，藉此推斷出行星的存在。
*2) 除利用徑向速度測量法發現的系外行星之外，美國太空總署的克卜勒任務利用凌日法（transit）發現1200多顆候選系外行星。凌日法是行星通過恆星時，用來測定恆星亮度減弱程度的方式。利用該法發現的多數行星皆離太陽系很遠（整體而言，比HARPS獵星器發現的行星遠6倍）。
*3) 質量為地球1至10倍的行星稱為超級地球。太陽系沒有這種行星，但是在其他恆星周遭似乎很常見。超級地球的發現令人振奮，因為它們具有岩石結構和水，可能有生命形式的存在。
*4) 其質量約為地球的17倍。
*5) 這些恆星是HARPS獵星器觀察到的，被認為可以精確測量徑向速度。]]> HP 天文 Thu, 02 Feb 2012 15:23:08 +0800 http://mepopedia.com/forum/read.php?571,19851,19851#msg-19851 http://mepopedia.com/forum/read.php?571,19851,19851#msg-19851
The dwarf was found using a technique called gravitational lensing. It is only the second dark dwarf ever seen, and it is by far the most distant.

The fact that so few dwarf galaxies are seen in our own cosmic neighbourhood has remained a conundrum in astronomy.

The study in Nature could explain it: they may be overwhelmingly dark matter.


[img]http://news.bbcimg.co.uk/media/images/57965000/jpg/_57965220_57965219.jpg[/img]

The light bent by a dark-matter-dominated galaxy can form what is known as an "Einstein ring"


Dwarf galaxies often occur in the periphery of larger galaxies, where they are known as satellites - the Milky Way may have many as well.

"According to the theory of galaxy formation, you'd expect thousands of these satellites," explained lead author of the study Simona Vegetti of the Massachusetts Institute of Technology.

"But if you look at the Milky Way we only find 30, so it's important to understand how many satellites are really there, and important to look at other galaxies other than the Milky Way," she told BBC News.

That will help determine if our cosmic neighbourhood of galaxies - the Local Group - is unusual, or if the theory of galaxy formation is incomplete.

Massive question
Dark matter is so named because it does not interact with light - it cannot be seen directly, as the stars and dust of the cosmos can.

However, it does have mass - making up 85% of the mass in the Universe - and the effects of that mass can be spotted.

Gravitational lensing is a technique in which an object that lies between Earth and a distant light source can actually act as a "lens"; the object's mass bends the distant galaxy's light, magnifying and distorting it.

By using computer models of how that magnification and distortion should work, the mass of the lensing galaxy - and where that mass is distributed - can be determined.

Gravity acting across vast distances does not seem to explain what astronomers see
Galaxies, for example, should fly apart; some other mass must be there holding them together
Astrophysicists have thus postulated "dark matter" - invisible to us but clearly acting on galactic scales
At the greatest distances, the Universe's expansion is accelerating
Thus we have also "dark energy" which acts to drive the expansion, in opposition to gravity
The current theory holds that 73% of the Universe is dark energy, 23% is dark matter, and just 4% the kind of matter we know well
The technique was recently used to develop the widest view of dark matter distribution in the Universe ever produced.

Dr Vegetti and colleagues in the US and the Netherlands have now used the Keck telescope in Hawaii to study the lensing caused by a distant elliptical galaxy called JVAS B1938+666.

They found a discrepancy in comparing with the image that their detailed computer model suggested should come from the system.

Something with a mass about 200,000,000 times that of our Sun is in the periphery of the image they see.

Yet that source of mass is not visible in the image of the galaxy itself.

"It's very hard to tell at the moment because the telescopes are just not powerful enough to see such dim galaxies so far away," Dr Vegetti said.

"But [the dwarf galaxy] is most likely dominated by dark matter, or maybe there are a few stars hiding here and there."

The team must continue the hunt for such satellites to get to the bottom of the dark mystery.

"We were kind of lucky that the first one we looked at also had a satellite," Dr Vegetti said.

"If we find other galaxies or satellites, it will tell us whether we need to change the properties of dark matter; if we don't find enough, then dark matter must be different from what we think."

BBC news
18 January 2012 Last updated at 19:34 GMT]]> mimizorro 天文 Thu, 19 Jan 2012 16:30:30 +0800